Copper alloys for electronic materials used in various electronic components such as connectors, switches, relays, pins, terminals and lead frames, are required to achieve a balance between high strength and high electrical conductivity (or thermal conductivity) as basic characteristics. In recent years, high integration, small and thin-type electronic components are in rapid progress, and in this respect, the demand for a copper alloy to be used in the components of electronic equipment is rising to higher levels.
From the viewpoints of high strength and high electrical conductivity, the amount of use of precipitation hardened copper alloys is increasing in replacement of conventional solid solution hardened copper alloys represented by phosphor bronze and brass, as copper alloys for electronic materials. In a precipitation hardened copper alloy, as a supersaturated solid solution that has been solution heat treated is subjected to an aging treatment, fine precipitates are uniformly dispersed, so that the strength of the alloy increases, the amount of solid-solution elements in copper decreases, and also, electrical conductivity increases. For this reason, a material having excellent mechanical properties such as strength and spring properties, and having satisfactory electrical conductivity and heat conductivity is obtained.
Among precipitation hardened copper alloys, Cu—Ni—Si alloys, which are generally referred to as Corson alloys, are representative copper alloys having relatively high electrical conductivity, strength and bending workability in combination, and constitute one class of alloys for which active development is currently underway in the industry. In this class of copper alloys, an enhancement of strength and electrical conductivity can be promoted by precipitating fine Ni—Si intermetallic compound particles in a copper matrix.
In order to obtain a Corson alloy which has high conductivity, strength and bending workability in combination and satisfies the requirements required in copper alloys for electronic materials of recent years, it is important to reduce the number of coarse second phase particles through appropriate compositions and production processes, and to control the grains to a uniform and appropriate particle size.
For such Corson alloys, in recent years, there has been an attempt to further enhance the characteristics thereof by adding Co.
Patent Literature 1 describes the following statements. Co forms a compound with Si similarly to Ni and increases mechanical strength. A Cu—Co—Si alloy is improved in terms of both mechanical strength and electrical conductivity when subjected to an aging treatment, as compared to a Cu—Ni—Si alloy. If it is allowable in view of cost, a Cu—Co—Si alloy may be chosen. Further, it is described that in order to suitably realize the characteristics, it is necessary that the grain size be adjusted to greater than 1 μm and less than or equal to 25 μm. The copper alloy described in Patent Literature 1 is produced by conducting, after cold working, a heat treatment for the purpose of recrystallization and a solution treatment, immediately conducting quenching, and conducting an aging treatment as necessary. It is described that it is desirable to perform a recrystallization treatment at 700° C. to 920° C. after cold working, and to perform cooling as rapidly as possible with a cooling rate of 10° C./s or greater, and that the aging treatment temperature is set to 420° C. to 550° C.
Patent Literature 2 describes a Cu—Co—Si alloy that has been developed for the purpose of realizing high strength, high electrical conductivity and high bending workability, and the copper alloy is characterized in that a compound of Co and Si and a compound of Co and P are present in the matrix phase, the average grain size of the matrix phase is 20 μm or less, and the aspect ratio of the sheet thickness direction to the rolling direction is 1 to 3. As a method for producing a copper alloy described in Patent Literature 2, a method of conducting cold rolling at a ratio of 85% or greater after hot rolling, annealing for 5 to 30 minutes at 450° C. to 480° C., conducting cold rolling at a ratio of 30% or less, and conducting an aging treatment at 450° C. to 500° C. for 30 minutes to 120 minutes, is described.